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Compressibility effects in a turbulent annular mixing layer. Part 2. Mixing of a passive scalar

Published online by Cambridge University Press:  02 November 2000

JONATHAN B. FREUND ,
PARVIZ MOIN  and
SANJIVA K. LELE
JONATHAN B. FREUND
Affiliation:
Center for Turbulence Research, Stanford University, Stanford, CA 94305, USA Present address: Mechanical and Aerospace Engineering, University of California, Los Angeles, USA.
PARVIZ MOIN
Affiliation:
Center for Turbulence Research, Stanford University, Stanford, CA 94305, USA
SANJIVA K. LELE
Affiliation:
Center for Turbulence Research, Stanford University, Stanford, CA 94305, USA
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Abstract

The mixing of fuel and oxidizer in a mixing layer between high-speed streams is important in many applications, especially air-breathing propulsion systems. The details of this process in a turbulent annular mixing layer are studied with direct numerical simulation. Convective Mach numbers of the simulations range from Mc = 0.1 to Mc = 1.8. Visualizations of the scalar field show that at low Mach numbers large intrusions of nearly pure ambient or core fluid span the mixing region, whereas at higher Mach numbers these intrusions are suppressed. Increasing the Mach number is found to change the mixture fraction probability density function from non-marching to marching and the mixing efficiency from 0.5 at Mc = 0.1 to 0.67 at Mc = 1.5. Scalar concentration fluctuations and the axial velocity fluctuations become highly correlated as the Mach number increases and a suppressed role of pressure in the axial momentum equation is found to be responsible for this. Anisotropy of scalar flux increases with Mc, and is explained via the suppression of transverse turbulence lengthscale.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 421 , 25 October 2000 , pp. 269 - 292
Copyright
© 2000 Cambridge University Press

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